Using a cellphone may increase the risk of a certain type of brain cancer, an international panel of experts said Tuesday, adding to a growing debate about whether a now nearly ubiquitous form of communication poses health risks.

The experts said cellphone radio waves are “possibly carcinogenic,” classifying them in the same risk category as lead, chloroform and coffee. The classification from the World Health Organization’s International Agency for Research on Cancer could lead the United Nations health body to look again at its mobile-phone guidelines, the scientists said.

The IARC panel did not conduct new research. Its findings, which will be published July 1 in the journal Lancet Oncology and in a few days online, came after reviewing the “available literature” on everything from microwave exposure to the environmental exposures of radio, television and wireless signals.

The group did not specify the risk cellphone users have of brain cancer, saying more detailed research is needed to identify a specific link. But the current research, the scientists said, is strong enough to support the classification.
The working group reviewed studies and concluded there was limited evidence that cellphones may cause glioma, a type of brain tumor that starts in the brain or spine.

“The conclusion means that there could be some risk, and therefore we need to keep a close watch for a link between cellphones and cancer risk,” Jonathan Samet, chairman of the IARC’s working group and a professor at University of Southern California, said in a statement.

The mobile-phone industry blasted the IARC’s decision, stating that the classification “does not mean cellphones cause cancer,” said John Walls, vice president of public affairs for the CTIA, a wireless telecommunications industry group based in the U.S.
Mr. Walls questioned the limited evidence from statistical studies, where conclusions could be drawn “even though bias and other data flaws may be the basis for the results.”

Dr. David Savitz, a professor of epidemiology at Brown University who has followed the issue but wasn’t part of the IARC working group, said the decision is surprising. As studies have tracked more people using cellphones for a longer period of time, the results have been “increasingly reassuring of the absence of a hazard,” he said.

A research project known as the Interphone study, released last year, compared adults diagnosed with certain brain tumors to similar people who had no tumors. Then researchers asked them all about their cellphone use. There were flaws in the research, however, and the study was inconclusive.
Dr. Savitz said that separately, data from cancer registries in Scandinavian countries that adopted cellphones early on haven’t suggested any increase in cancer risk. Even if it took a long time before cellphone exposure produced cancer, experts would still expect to see “the beginnings” of an increase in cancer rates, he said.

Combining all the different types of evidence, it’s “hard to see how you come to a conclusion” that there’s a risk, he said, adding that because the stakes are so high, the issue shouldn’t be dropped. “You have to be prudent about an exposure that’s so widespread and so novel,” he says.

Globally, there are an estimated five billion cellphone subscriptions, the IARC said, citing data from the International Telecommunication Union. The global population is currently about 6.9 billion. The number of U.S. wireless subscribers, as counted by number of connections, was 302.9 million in December 2010, compared to 33.8 million in 1995, according to CTIA.

U.S. mobile users log 663 voice minutes per month and 737 text messages, according to first-quarter data from market researcher Nielsen Co. That compares to 679 voice minutes and 25 text messages in the first quarter of 2005, the first time Nielsen tracked such data.